1. Field of the Invention
This invention refers to an apparatus for testing the color separations of a multicolor print, comprising a pair of press rollers being mounted in a frame and constituted by rollers which can be lifted off each other, through the roller gap of which an image-bearing element, consisting of a support foil with an exposed, photosensitive layer, with a color foil, consisting of a color-bearing foil with a color layer, being placed on this element, is fed such that portions of the color layer adhere to the tacky areas of the image-bearing element.
2. Description of Prior Art
In multicolor printing it is advantageous to test the quality of the color separations prior to the actual printing without having to make a test printing, so that any corrections which may be necessary can be carried out and registration and positioning can be controlled. Such a testing is carried out in such a manner that corresponding halftone color separations are made from the individual originals and said color separations are copied by means of an appropriate exposure onto the photosensitive layer of an image-bearing element. In case of a preferred testing print material the photosensitive layer consists of a photopolymerizable material which is tacky at least at its surface and which is polymerized by exposure such that it loses its tackiness in the exposed areas. Then, a color-bearing foil is pressed onto the thus exposed image-bearing element such that the color layer thereof adheres to the unexposed sections due to their tackiness. Therein, the color of the color layer corresponds to the color of the color separation to be tested so that the image-bearing element carries a positive image of the color separation to be tested. On top of the image-bearing element there is then applied a second photosensitive layer as a laminate, and then the image-bearing element is exposed through a halftone color separation belonging to a second color of the original. Onto said second exposed photosensitive layer then a color-bearing foil with a second color is pressed so that to the unexposed areas again portions of the color foil adhere after the latter is peeled off, and a positive two-color image of the original is obtained. Corresponding to the colors to be used in making the print, additional photosensitive layers are applied, exposures are performed through the additional halftone color separations, the exposed layers are supplied with corresponding color applications by pressing the color layers thereonto, until a multicolor image corresponding to the original is obtained. Testing methods of said kind and photosensitive layers to be used in said testing methods are known from the German Patent Specification 26 23 850 (parallel U.S. Pat. No. 4,304,839), from the European laid-open print 243 933 and from the U.S. Pat. No. 4,356,253. Suitable color-bearing foils have been described in the German Patent Specification 36 25 014 (parallel U.S. Pat. 4,806,451) and in the German laid-open print 37 06 528 (parallel U.S. Pat. No. 4,902,363). In an analogous manner, also photosensitive layers can be used which only become tacky on exposure and which are known from the German Patent Specification 34 29 615 (parallel U.S. Pat. No. 4,604,340).
A particular problem in performing the color testing method lies in the fact to apply and press the color foil onto the corresponding exposed photosensitive layer of the image-bearing element such that after peeling off the color foil the desired image of the color separation of the original is obtained.
If by the apparatus of the kind mentioned hereinbefore for instance the color separations of a four-color print are to be tested, the image-bearing element with a separately applied and exposed photosensitive layer, together with the corresponding color foil must be transported four times through the roller gap of the pair of press rollers, which requires a certain dexterity due to the necessary manipulation and which is time-consuming.